The present invention relates to integrated-optic modulators and particularly to a polarization-selective integrated optic phase modulator suitable for use in coherent communications, optical signal processing, fiber sensors and waveguide sensor systems.
Typically, integrated-optic waveguide modulators in LiNbO.sub.3 substrates exhibit strong polarization dependence. This is primarily due to the strong anisotropy in the material and the resulting difference in electro-optic coefficients for different crystal axis orientations. In general, both the transverse electric (TE) field (or horizontal polarization component) and the transverse magnetic (TM) field (or vertical polarization component) of an input polarized light are phase modulated by the application of an electric field to a channel waveguide in a LiNbO.sub.3 substrate. By suitably utilizing a combination of vertical and horizontal electric fields produced by appropriate electrode patterns, as taught in U.S. Pat. No. 4,291,939, it has been shown that the overall TE and TM phase modulation efficiencies can be equalized, thus producing a `polarization independent` phase modulator. However, to date, no known prior art integrated-optic phase modulator has been developed which can selectively phase modulate only one of the two polarization modes or components of an input polarized light.